Article and method of coating continuous filament



Aug. 26, 1969 w gsgp. ET AL 3,463,652

ARTICLE ANDMETHGD OF COATINGCONTINUOUS FILAMENT Filed Aug. 5. 1968 'JOSEPH C. WHITESEL STANLEY N. WEISSMAN INVENTORS TTORNEY United States Patent 3,463,652 ARTICLE AND METHOD OF COATING CONTINUOUS FILAMENT Joseph Collichio Whitesel, Waynesboro, Va., and Stanley Norman Weissman, Cedar Grove, N.J., assignor to W. R. Grace 8: Co., New York, N.Y., a corporation of Connecticut Continuation-impart of abandoned application Ser. No. 495,049, Oct. 12, 1965. This application Aug. 5, 1968, Ser. No. 757,185

Int. Cl. C08d 13/24; B44d 1/22 U.S. Cl. 117-7 13 Claims ABSTRACT OF THE DISCLOSURE The disclosed invention is for a continuous strand or filament having the ability to hold knots which includes an oriented poly (alpha-olefin) fiber having a specified tenacity and formed of a plurality of filaments having a denier from about 25 to about 1,200; and a foamed thermoplastic coating disposed about the oriented poly (alphaolefin) fiber. The thermoplastic coating has an outer diameter of from about 25 to about 1,000 mils and is formed of a foamed themoplastic having a specific gravity of from about 0.1 to about 0.7 and having a melting point below the melting point of the oriented poly (alpha olefin) fiber. The filament is formed by extruding a foam coating on pretensioned fibers, cooling the coating and releasing the tension on the fibers.

This application for United States Letters Patent is a continuation in part application of U.S. patent application Ser. No. 495,049, filed Oct. 12, 1965, now abandoned.

This invention relates to a novel foam covered fiber and to a process for preparing same.

It is known in the art that various poly (.alpha-olefins), such as polyethylene and polypropylene, can be fabricated into filaments. The cost and physical properties of the filaments in many instances make them competitive with the presently utilized natural fibers. However, a serious drawback to the synthetic poly (alpha-olefin) filaments is the fact that the filaments have a low coefficient of friction which renders the product undesirable whenever knots are required in the filament. For example, when using heavy filaments similar to binder twine for joining pieces together, the knots made in the filaments can generally be pulled out with simple hand pressure. Accordingly, such filaments have not found widespread use where the ability to knot is an important factor. Quite obviously, if a filament could be produced having the strength characteristics of the poly (alpha-olefin) with an improved ability to hold knots, it would receive widespread acceptance in the art.

It is an object of the present invention to provide a continuous strand or filament. A further object is to provide a coated fiber which has the ability to hold knots. A still further object it to provide a simple and inexpensive process for coating a fiber. Other objects will become apparent as the description of the invention proceeds.

These objects are accomplished by the present invention which provides a continuous strand or filament havinga diameter of from about 25 to about 1,000 mils and comprising an oriented poly (alpha-olefin) fiber coated p CC with a foam of a thermoplastic having a melting point below the melting point of poly (alpha-olefin); the said fiber comprising at least two filaments having a denier of from about 25 to about 1,200 and the said foam having a specific gravity of from about 0.1 to about 0.7.

In a preferred embodiment of the present invention, the continuous strand or filament has a diameter of from about 35 to about 750 mils, the individual filaments have a denier of from about 40 to about 600 and the foam has a specific gravity of from about 0.15 to about 0.6. In a still more preferred embodiment, the continuous strand or filament has a diameter of from about 50 to about 5-00 mils, the individual fibers have a denier of from about 50 to about 300 and the foam has specific gravity of from about 0.2 to about 0.5.

The present invention also provides a process for the preparation of a foam coated fiber which comprises applying stress to an original poly (alpha-olefin) fiber having a denier of from about 25 to about 1,200, applying a coating of a molten thermoplastic containing a blowing agent at a temperature above the decomposition temperature of the blowing agent and below the melting point of said fiber, cooling the coating and thereafter removing the stress from the fiber.

The term continuous merely signifies a unitary structure which has two dimensions which are very small as compared to the third dimension (length). It is synonomous with the term mom-filament as employed in the textile field.

The term oriented is generally used as in the textile field to mean a structure which has been stretched to orient or axially align the molecules. The degree of orientation, of course, will depend upon the amount of stretch imparted to the filament prior to the coating procedure and it will, in general, be that of a fiber stretched from about 3 X to about 12X its normal length at a temperature of 260 F. Preferably the material is stretched from about 6X to about 9X its normal length at 260 F. More accurately, however, the term oriented is applied to a stressed fiber having a tenacity in the range of about 4 to about 12 grams per denier and preferably in the range of about 7 to about 10 grams per denier. An original fiber may be one having a tenacity of about 0.5 grams per denier.

The poly (alpha-olefin) utilized in the present invention are polymers from one or more alpha-olefins such as ethylene, propylene, butene-l and the like. Preferably the polymers are high density polyethylene or polypropylene. The preparation of such polymers are given in U.S. Patents 2,825,721; 2,911,304; 3,006,829; 3,062,801 and 3,- 078,250 and others. The term coated signifies that the fibers in the central portion of the filament are completely enclosed within the foam. The expression thermoplastic designates any polymer which becomes soft and melts with heating. A particularly preferred thermoplastic is low density polyethylene although high density polyethylene, polyvinyl chloride and other thermoplastics are likewise operable. The only requirement for the thermoplastic is that it melts below the melting point of the poly (alpha-olefin) fiber and that it have a sufficiently high melting point so as to expand the blowing agent employed.

The expression blowing agent is used in its conventional sense to mean any material suitable for incorporation into plastic to form bubbles therein by the application of heat, reduction in pressure and the like as is known in the art. Among the suitable blowing agents which may be used in the practice of the present invention are gases such as nitrogen or the very volatile liquid fluorocarbons such :as l,2-dichlorotetrafiuoroethane and the like. The more preferred blowing agents, however, are the chemical agents which decompose with the liberation of a gas as one of the decomposition products. Such materials include barium azodicarboxate, 4,4-oxybis (benzenesulfonylhydrazide), bis-benzenesulfonyl hydrazide, 4,4-oxybis (benzenesulfonyl semicarbazide), dinitrosopentamethylene-tetramine, trihydrazino-syn.-triazine, and 1,l-azobisformamide. Other blowing agents are disclosed in US. Patents 2,532,243; 2,804,435; 2,819,231; 2,927,904; 2,948,664 and others. A particularly preferred blowing agent is 4,4-oxybis(benzenesulfonylhydroazide).

While the amount of blowing agent in the plastic is not critical, it is generally desirable to employ from about 0.05 to about by weight, based on the weight of the polymer, when the blowing agent is a chemical blowing agent. Preferably, from about 0.2 to about 6% by weight of blowing agent is employed.

The invention is hereinafter more fully described by reference to the drawing which illustrates preferred embodiment of the present invention:

FIGURE 1 is a side view of the foamed continuous strand or filament produced in accordance with the present invention in which a portion of the foam coating is cut away to show the fiber in the interior of the filament; and

FIGURE 2 shows an enlarged cross section of the foamed product produced in accordance with the present invention.

In the figures, fiber 1 in the interior of the strand or filament is completely covered with foam coating 2. The foamed coating allows the filament to be firmly knotted without slipping.

The following examples are given to illustrate the invention and are not intended to limit it in any manner. All parts are given in parts by weight unless otherwise indicated.

Example 1 A foamable coating mixture is prepared by dry blending a polyethylene homopolymer having a specific gravity of 0.920 and a melt index of 3.0, with 2% by weight, based on the weight of the polymer, or 4,4-oxybis(benzenesulfonylhydrazide) for 10 minutes in a double cone blender.

A commercial oriented (8X at 260 F.) polypropylene fiber containing 12 ends of 50 denier per end (total denier 600) is extrusion coated with the foamable mixture. The extrusion coating is carried out using a Sterling 1 /2" diameter extruder with a Davis Standard cross head die for wire coating. The extruder conditions are as follows:

Extruder temp., F., Zone 1 303 Extruder temp., F., Zone 2 321 Head temp., F., Zone 3 277 Die temp., F., Zone 4 273 Screw speed, r.p.m. 40 Head pressure, p.s.i 1700 Coating speed, f.p.m. 128

The resulting coated filament has a diameter of 100 mils and the specific gravity of the foam jacket is 0.6 g./cc. The break strength of the coated filament is pounds and it is suitable for tying small packages or for decorative purposes if the coating is colored.

Example 2 A foamable coating mixture is prepared by dry blending a polyethylene homopolymer having a specific gravity of 0.920, and a melt index of 3.0 with 4% by weight, based on the weight of the polymer, of 4,4-oxybis(benzenesulfonylhydrazide) for 10 minutes in a double cone blender.

A commercial oriented (8X at 250 F.) polypropylene fiber containing 128 ends of 70 denier per end (total denier 8,960) is extrusion coated with the foamable mixture. The extrusion coating is carried out using a Sterling 1 /2" diameter extruder with a Davis Standard cross head die for wire coating. The extruder conditions are as follows:

Extruder temp., F., Zone 1 272 Extruder temp., F., Zone 2 300 Head temp., F., Zone 3 218 Die temp., F., Zone 4 217 Screw speed, r.p.m 30

Head pressure, p.s.i 1,150 Coating speed, f.p.m.

The resulting coated filament has a diameter of 136 mils and a specific gravity of 0.9460 g./-cc. The specific gravity of the foam jacket is 0.43 g./cc. The break strength of the filament is 140 pounds and it is suitable for use as binder twine. Unlike the uncoated fiber, the coated filaments knots easily and the the knots are retained up to the break strength of the filament.

Example 3 The procedure of Example 2 is repeated with the exception that the polypropylene fiber is replaced with an oriented polyethylene fiber having 12 ends of 50 denier per end (total denier 600). The polyethylene fiber is formed of polyethylene homopolymer having a specific gravity of 0.960 and a melt index of 0.2.

Substantially the same results are obtained as in Example 2.

Example 4 The procedure of Example 2 is repeated with the exception that 1% by weight, based on the weight of the polymer, of phythalocyanine green is dry blended with the ingredients of the foamable mixture.

The product is the same as that in Example 2 with the exception that it is colored green.

Example 5 The product of Example 2 is repeated with the exception that a mixture of blowing agents are employed in the foamable mixture and an increased quantity of blowing agent is used. The mixed blowing agent is 2% by weight, 4,4'-oxybis(benzenesulfonylhydrazide) and 2% by weight of azodicarbonamide.

The resulting product is essentially the same as that of Example 2.

Example 6 Extruder temp., F., Zone 1 302 Extruder temp., F., Zone 2 325 Head temp., F., Zone 3 269 Die temp., F., Zone 4 277 Screw speed, r.p.m. 60 Head pressure, p.s.i 750 Coating speed, f.p.m. 720

The resulting coated filament has a diameter of 100 mils and the specific gravity of the foam jacket is 0.5 g./cc. The break strength of the coated filament is 18 pounds and it is suitable for tying small packages.

Typical conditions for preparation of oriented polypropylene filaments similar to those used in Examples 1, 2, 4, 5, and 6 are listed in Table I.

formed of a plurality of filaments, said filaments having a denier from about 25 to about 1,200; (b) applying a coating about said stressed poly(alpha- TABLE I Processing Conditions Fiber Properties E t t o q '7 A I? $1 x ruder Tempera mes, F a a k; a g g q A A q a, v v .1. V F

:5. v =3 51 E 5. Eu- E a Q a:

a a e a s 2 a 3 a a a s a as e s .2 a a z; a

N N N Q Q h a. U Q Q Q is a Q 2 0 Q a Q Q a 430 470 500 500 500 23 1, 500 99 650 52 0. 5 650 750 30 500 260 y 3-hole 799/3 9. 4 5. 4 430 470 500 500 500 22 1, 500 90 810 53 0. 5 650 750 60 500 260 6% 594/ 10. 1 7. 7 430 470 500 500 500 22 1, 600 85 800 51 0. 5 800 900 60 500 260 536/10 10. 7 8. 9

While in the foregoing examples substantially unmodified materials are employed, it is obvious that delustrants, fillers, flame retardant materials and the like may be employed in the process without substantial alteration of the process conditions or the properties.

The products produced in accordance with the present invention can be employed wherever twines, cords, ropes or the like are presently used.

Many equivalent modifications will become apparent to those skilled in the art from a reading of the foregoing without a departure of the invention concept.

What is claimed is:

1. A continuous strand having the ability to hold knots which comprises:

(a) an oriented poly(alpha-olefin) fiber having a tenacity in the range from about 4 to about 12 grams per denier and imparted by stretching an original fiber, said oriented poly(alpha-olefin) fiber formed of a plurality of filaments, said filaments having a denier from about to about 1,200 and (b) a foamed thermoplastic coating disposed about said oriented poly(alpha-olefin) fiber, said thermoplastic coating having an outer diameter of from about 25 to about 1,000 mils and formed of a foamed thermoplastic having a specific gravity of from about 0.1 to about 0.7 and having a melting point below the melting point of said oriented poly- (alpha-olefin) fiber.

2. The continuous strand of claim 1 wherein the denier of the filaments is from about 40 to about 600; the outer diameter of the foamed thermoplastic coating is from about 35 to about 750 mils; and the foamed thermoplastic specific gravity is from about 0.15 to about 0.6.

3. The continuous specific gravity of claim 1 wherein the denier of the filaments is from about 50 to about 300; the outer diameter of the foamed thermoplastic coating is from about 50 to about 500 mils; and the foamed thermoplastic specific gravity is from about 0.2 to about 0.5.

4. The continuous strand of claim 2 wherein the tenacity imparted by stretching an original fiber is from about 7 to about 10 grams per denier.

5. The continuous strand of claim 3 wherein the tenacity imparted by stretching an original fiber is from about 7 to about 10 grams per denier.

6. The continuous strand of claim 3 wherein the filaments are formed of a plurality of oriented polypropylene fibers; and the foamed thermoplastic is polyethylene.

7. A process for the preparation of a continuous strand having the ability to hold knots which comprises:

(a) applying stress by stretching an original fiber of poly(alpha-olefin) to a tenacity of about 4 to about olefin) fiber of a molten thermoplastic containing a blowing agent while at a temperature above the decomposition temperature of the blowing agent and below the melting point of said oriented poly(alphaolefin) fiber;

(c) foaming the coating of molten thermoplastic to a foam specific gravity of about 0.1 to about 0.7; and an outer diameter of from about 25 to about 1,000 mils;

(d) cooling the coating to harden the foamed thermoplastic and thereafter (e) removing the stress applied to said oriented poly (alpha-olefin) fiber after foaming and cooling the thermoplastic coating thereon.

8. The process of claim 7 wherein the denier of the filaments is from about 40 to about 600; the outer diameter of the foamed thermoplastic coating is from about 35 to about 750 mils; and the foamed thermoplastic specific gravity is from about 0.2 to about 0.5.

9. The process of claim 7 wherein the denier of the filaments is from about 50 to about 300; the outer diameter of the foamed thermoplastic coating is from about 50 to about 500 mils; and the foamed thermoplastic specific gravity is from about 0.2 to about 0.5.

11. The process of claim 8 wherein the tenacity imparted by stretching an original fiber is from about 7 to about 10 grams per denier.

12. The process of claim 9 wherein the tenacity imparted by stretching an original fiber is from about 7 to about 10 grams per denier.

10. The process of claim 7 wherein the filaments are a plurality of oriented polypropylene fibers each having a denier of from about 50 to about 300; the molten thermoplastic is a polyethylene polymer; and the blowing agent is 4,4-oxybis (benzenesulfonylhydrazide).

13. The process of claim 10 wherein the tenacity imparted by stretching original fibers of polypropylene fibers is from about 7 to about 10 grams per denier.

" References Cited UNITED STATES PATENTS 3,327,339 6/1967 Lemelson 161-175 3,244,545 4/1966 Marzocchi et al 1l7-7 X 3,068,532 12/ 1962 Higgins 264-47 2,862,282 12/ 1958 Beebe 264-47 2,835,927 5/1958 Henning 264-47 ALFRED L. LEAVITT, Primary Examiner A. GRIMALDI, Assistant Examiner US. Cl. X.R.

12 grams per denier, said poly(alpha-olefin) fiber 57-149, 162; 117-138.8; 161-175; 264-174 

